A worldwide study found that trees need two to four years to recover from drought and resume normal growth rates, which means forests would not store as much carbon as climate models have assumed, says the University of Utah. “If forests are not as good at taking up carbon dioxide, this means climate change would speed up,” says lead author William Anderegg, an assistant biology professor at the university. The team of scientists examined tree-ring data taken at 1,300 sites in forests around the world to assess the rate of recovery from severe droughts that have occurred since 1948. On average, it took two to four years for trunk growth to return to normal. In the first year after a drought, growth was 9-percent slower than normal and 5-percent slower in the second year.
Recovery took longest for trees in dry ecosystems and among pine and species with low hydraulic safety margins. The reasons are unknown but causes could include loss of foliage, increased damage by pests and disease, and permanent damage to vascular systems that transport water inside the tree. Anderegg says rising average temperatures “suggest quite strongly that the western regions of the United States are going to have more frequent and severe droughts, substantially reducing forests’ ability to pull carbon from the atmosphere.”